Nuts are typically fed through a nut feed passage by reciprocating a nut feed pawl having a finger received in the nut bore. The nut feed pawl is typically pivotally mounted on a feed mechanism, wherein the nut feed pawl is biased by a spring, pneumatic or hydraulic pressure or a positive linkage to reciprocate through the nut feed passage. The nut bore may be threaded or unthreaded to receive a thread forming or thread rolling male fastener, such as a bolt or screw. Nuts are fed through a nut feed passage for various purposes including, but not limited to, secondary operations, such as interconnecting the nuts in a strip, and installation. However, the nut feed pawl may deform or damage the nut bore during feeding of the nuts through a nut feed passage making it difficult or impossible to thread a male fastener into the nut bore. For example, the nuts may be jammed or cocked in the nut feed passage and the force of the finger of the nut feed pawl in the thread cylinder may be sufficient to damage a threaded nut bore or an unthreaded nut bore.
This is a particular problem with self-attaching nuts, including pierce, clinch and weld nuts, wherein the nut is permanently attached to a metal panel because the entire nut and panel assembly may have to be scrapped if the nut bore cylinder is damaged. In many applications, such as automotive applications, several self-attaching nuts are simultaneously attached to a panel, such as a bracket, frame or vehicle body component and the male fasteners are typically threaded into the nuts with a torque wrench. Thus, if the thread cylinder (threaded or unthreaded) of one of the nuts is damaged or distorted, a male fastener may crossthread in the nut bore or it may not be possible to thread the male fastener into the nut bore, requiring scrapping or retrofitting the entire assembly. As used herein, the term “nut” includes any female fastener having a threaded or unthreaded bore. Thus, there has been a long felt need for a method of feeding nuts through a feed passage using a feed pawl which does not engage the nut bore, eliminating damage or distortion of the nut bore.
Various attempts have been made by the Applicant and others to eliminate damage to the nut bore or thread cylinder through feeding of nuts through a nut feed passage, including providing notches in the side faces of the nut and feeding the nuts with two feed pawls or ratchets on opposed sides of the nuts which feed the nuts to a fastener installation head or for secondary operations, such as interconnecting the nuts in a strip, as disclosed for example in PCT Application WO 03/016727 A2 filed Jul. 31, 2002 and assigned to the assignee of this application. However, such methods of feeding nuts require additional space, particularly for fastener installation heads where additional space is not available and such methods are not always reliable because the use of two feed pawls or ratchets must be balanced to avoid cocking of the nuts during feeding. Further, such methods require complex feed mechanisms and substantial modification of the fastener and the feed mechanism. It would thus be desirable to feed nuts through a feed passage without contacting the nut bore, but with minimal modification of the feed pawl and the nut. The method of feeding nuts, nut feed pawl and nut configuration of this invention solves the problem of nut bore distortion or damage during feeding with minimal modification of the feed pawl and nut.